Cara Ocobock, Ph.D.

We have a new publication out in the American Journal of Human Biology looking at the relationship between resting metabolic rate and thyroid hormones (TSH, fT₃, and fT₄) among reindeer herders and office workers in Northern Finland. It is open access and can be found here.

We found that female reindeer herders exhibit a pattern different from all other participants in this study such that they had higher than expected RMRs, significantly higher free T₃ and TSH, and a positive correlation between free T₄ and RMR.

These results demonstrate that female reindeer herders are remaining physiologically resilient, potentially to protect reproductive capacity, in response to a drastically warming climate. We are also potentially witnessing a transition among male reindeer herders who are physiologically responding to the rapidly warming climate, as demonstrated by their highly variable RMRs. Finally, this work highlights the complex interaction between THs and the environment as demonstrated by the numerous environmental inputs (temperature, climate change, selenium levels, and local policy) experienced by the participants in this study. Future work will examine seasonal differences in RMR and TH dynamics as well as the impact of the menstrual cycle among herders and office workers providing greater insight into cold climate physiology and the metabolic response to climate change.

I will be upfront in that I had absolutely nothing to do with this design and data collection of this study. Lead author, the amazing and brilliant Courtney Manthey, led this study and she wanted to better understand if there is a connection between early age at menarche and Polycystic Ovary Syndrome (PCOS). She was also interested in if there are potential evolutionary reasons for the existence of PCOS, but that didn’t make it into the paper. She asked me to collaborate in the interpretation of the results in an energetics framework. I don’t say this to wash my hands of this work – quite the opposite! More that I only had the tiniest of roles in this work and credit goes to Courtney.

She found that early age at menarche is associated with developing PCOS, but we still have a lot of unanswered questions. In terms of evolution, an early age at menarche would mean growth stops sooner than it would have otherwise. This would lead to smaller body sizes and a decreased energetic demand to maintain that small body – a potential benefit in our ancestral environments. This might help explain the high heritability of PCOS, but again, lots of work needs to be done to confidently say this.

This research was the direct result of a conversation at a conference. Conversations and ideas fly at conferences, but I am not sure I have ever had one go from just talking to collecting data within a few short months.

Our collaborator, Dr. Alexandra Greenwald, is an archaeologist interested in what women were doing and the technologies they used to not only care for children, but also maintain their subsistence activities. For this study, looked at the metabolic cost of gathering acorns. then we compared that cost to the cost of gathering acorns while carrying a “child” (it was a sandbag) in a sling and then in a cradle that can be worn on the back or set down. We measured metabolic cost as well as caloric return on acorns gathered.

Results were not significantly different for this study, but we were also only able to measure among six participants. However, the trends do indicate that the cradle improved foraging efficiency, demonstrating the importance of improved technology enabling women to maintain their activities while also caring for children. This is a great basis and model for examining the impact of early technologies on foraging efficiency as well as the importance and impressive nature of women’s work.

This work was one of those fun collaborations that kind of came out of nowhere. Lead author, Alvaro, contacted me out of the blue one day asking if there were a way I could help him estimate the metabolic costs of long overseas journeys like the ones that ancient peoples did when traveling to and inhabiting Hawaii and New Zealand. For this model, we focused particularly on just resting metabolism as that was a key first step. We hope to add activity costs in the future when we are able to get some better empirical evidence of the metabolic cost of this particular kind of seafaring.

Alvaro brought the calculating, modeling, and coding skills. Myself and Dr. Alexandra Niclou managed the metabolic work. Atholl and Scott provided the geographic and archaeological contexts for this work. We found, that following Bergmann’s and Allen’s Rules, that individuals with larger body sizes would have faired better during the harsh sea conditions of these long journeys. The larger body sizes would have meant less heat loss in wet and windy conditions, and it seems females faired better than males in these models.

It was a beast of math and estimates on estimates, of course, making our certainty with these numbers lower than we might like. However, this is the first work of its kind and provides a basis for future work to refine the model and improve its accuracy. So, consider this the first step in trying to determine the metabolic/physical demands of seafaring and prehistoric overseas colonization.

I am very behind on updating the website with new publications, so these will be quick summaries.

This research was conducted by Dr. Alexandra Niclou and her team in Samoa, and looked at substrate metabolism in brown adipose tissue (BAT). The Samoan individuals in this study exhibited brown adipose tissue activity, and their BAT metabolized a mix of glucose and fatty acids.

This is different from what we have seen in other populations for whom BAT substrate metabolism has been documented. For example, BAT among the Sakha of Siberia seems to preferentially use glucose. While reindeer herders in Finland exhibit BAT that uses a majority fatty acids.

This work demonstrates that there is a great deal of individual in interpopulational variation in BAT activity and substrate utilization. We still do not know why variation in substrate utilization exists. It could be driven by dietary differences, mitochondria level differences, and potentially even the intriguing possibility that BAT has anaerobic and aerobic metabolic components.

This is the big review article I wrote for Annual Review of Anthropology covering the ways humans have adapted and acclimatized to extreme environments. I talk about the class big three (hot, cold, high altitude) and then discuss emerging extremes such as climate change and socioeconomic disparities.

This is a great article for undergraduate classes because of its scope, citations, and accessibility.